Clinical Nutrition Assessment of ISS Astronauts, SMO-016E (Clinical Nutrition Assessment) - 01.10.18

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Nutritional assessments of astronauts before, during, and after spaceflight ensure adequate intake of energy, protein, and vitamins during missions. Scientists use the information to understand the connections between nutrition and human health during space flight, and to develop effective dietary strategies to reduce adverse health impacts.
Science Results for Everyone
Feel it in your bones. Data from this investigation found crewmember bone biochemistry consistent with previous studies. Bone and calcium regulation appears intact during space flight, regardless of an individual’s sex. Diet, exercise devices, and pharmacological countermeasures can help to mitigate the weightlessness-induced bone loss. Despite consistent, significant decreases in serum and urinary magnesium immediately after space flight, tissue stores of the mineral are maintained after flight, and serum and urinary magnesium actually increased when measured in inflight samples. This suggests there is no general cause for concern about magnesium deficiency during long-duration space exploration, but questions remain about the effect of exercise on bone strength and fracture risk and the role of magnesium and how much of it crewmembers need in their diet.

The following content was provided by Scott M. Smith, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details


Principal Investigator(s)
Scott M. Smith, Ph.D., NASA Johnson Space Center, Houston, TX, United States

Information Pending

Information Pending

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)

Research Benefits
Information Pending

ISS Expedition Duration
November 2000 - December 2002; November 2002 - May 2003; April 2003 - April 2007

Expeditions Assigned

Previous Missions
Similar studies were completed during NASA/Mir.

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Experiment Description

Research Overview

  • The Clinical Nutritional Status Assessment measures dietary intake, body composition, protein, bone, iron, mineral, vitamin, and antioxidant status. Currently, it is a medical requirement for U.S. crewmembers on-board the ISS.

  • Blood and urine samples are collected pre and postflight from the astronauts and analyzed for over 60 diagnostic compounds, vitamins, and minerals. Weekly dietary intake and body mass are measured in-flight; these measurements are used by the crew flight surgeon to adjust the astronauts' food intake.

  • The results of data analysis are used both to understand the connections between nutrition and human health during space flight, and to develop effective dietary strategies to reduce adverse health impacts (including bone loss, loss of important vitamins and minerals, and increased genetic damage from radiation).

To provide nutritional recommendations to crew members for long-duration space travel, we need to better understand how nutritional status and general physiology are affected by the microgravity environment. Dietary intake during space flight has often been inadequate, and this can greatly compromise nutritional status. Data from both short- and long-duration space flights provide evidence that energy intake is typically 30-40% below World Health Organization recommendations, but energy expenditure is typically unchanged or even increased. This imbalance may explain some of the observed negative changes in overall nutritional status during flight. However, blood concentrations of some nutrients, such as vitamin D, continue to be low even when astronauts receive supplements during flight. The space environment itself results in physiologic changes that can alter nutritional status. For example, changes in iron metabolism are closely associated with blood chemistry alterations during space flight. Similarly, increased levels of radiation and oxidative stress during flight likely contribute to decreased antioxidant status and genetic damage during or after space flight.

There are six components to the research program.

  • The food system provides a six to ten-day menu cycle; before each mission, crew members participate in food-tasting sessions, and dietitians plan menus that will use crew choices and best fulfill the defined nutritional requirements for space flight.

  • During flight, crew members are asked to record their dietary intake once per week using a Food Frequency Questionnaire (FFQ) designed for use with the space flight food system. The FFQ is designed to obtain a near real-time estimate of intakes of energy, protein, water, sodium, calcium, and iron, as well as to collect information about vitamin supplement use and any crew comments. The questionnaire inputs from the astronauts are transmitted to the ground and results are calculated and reported to the flight surgeon within 24 to 48 hours.

  • Body mass is determined pre, post, and inflight, while body composition is determined pre and postflight using laboratory measurements.

  • Blood and urine samples are collected pre and postflight for analysis of whole blood, plasma, serum, and various analytes; blood pH and ionized calcium levels are measured inflight using finger sticks.

  • Biochemical analysis of the blood and urine samples are performed at Johnson Space Center using standard laboratory methods.

  • Statistical analysis of the analytical results is performed to detect differences in nutritional status from preflight to postflight.
Body mass and body composition analyses were performed using an X-ray absorptiometer that was equipped with a fan beam densitometer. In-flight body mass measurements require two astronauts, one to take measurements and the other to record the data. The measurements were obtained using a body-mass measuring device; this device exerts a known force on the body and measures body acceleration. Body mass was then calculated. Standard medical finger sticks and capillary tubes were used to obtain blood samples for input into an analyzer unit onboard. A single astronaut performed the blood collection and analysis procedure. The FFQ program, which was loaded on station computers, was used to input food consumption information on a weekly basis.

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Space Applications
Nutritional monitoring is vital to ensuring crew health during long-duration space flight. The results are being used to identify specific effects of microgravity on nutrient-depended processes such as vitamin uptake, antioxidant production, and metabolism of iron. Alterations to nutrient assimilation in microgravity are also important for studies of bone loss while in microgravity.

Earth Applications
Increased understanding of the connections between nutrition and bone loss has potential value for patients suffering bone loss on Earth.

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Operational Requirements and Protocols
Data collection is completed on every ISS expedition as it is a requirement for medical monitoring during the flight. Body mass, FFQ, and blood sample data is downlinked on a weekly basis for review by the flight surgeon.
Astronauts use the FFQ program to record their menu choices during the week as other operational duties and tasks allow. Astronauts also include vitamin supplements (such as Vitamin D) with their daily food intake. Body mass measurements are taken each week by each US astronaut using the body-mass measuring device. Blood samples are analyzed using finger sticks and the onboard analyzer to monitor blood pH and ionized calcium levels on a weekly basis. This information is recorded and downlinked each week to the flight surgeon, who uses the information to track the nutritional status of each astronaut. If decreases in body mass or nutritional balance are noted, the flight surgeon may advise the astronaut on measures to compensate.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

The Nutritional Status Assessment project examined many biomarkers in blood and urine samples collected from ISS crewmembers.  Analysis of the bone biochemistry is consistent with previous studies, despite confounding factors, including sex, dietary intake, exercise devices, pharmacological countermeasures, and mission duration, the regulation of bone and calcium homeostasis appears intact. Bone breakdown is increased in weightlessness, and this can be countered by an exercise-induced increase in bone formation.  Nutritional support is integral to success of microgravity countermeasures.  Important questions remain about the effect of the exercise-induced remodeling on bone strength and fracture risk.
We know that magnesium is a critical nutrient, with many important functions. On Earth magnesium homeostasis can be altered by disease and medication use, the Nutritional Status Assessment project documented that despite consistent and significant alterations in urinary magnesium after space flight, tissue stores of the mineral are maintained, and inflight data reveal increased serum and urinary magnesium. Thus, there is no general cause for concern about magnesium deficiency in long-duration space explorers, however acute effects of exercise or extravehicular activity on magnesium status and understanding the source of the increased urinary and serum magnesium still needs to be investigated. Additional studies are needed to better understand the role of magnesium in long-duration space explorers and to better define the nutritional requirement for magnesium in future space explorers.

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Results Publications

    Smith SM, Heer MA, Shackelford LC, Sibonga JD, Ploutz-Snyder LL, Zwart SR.  Benefits for bone from resistance exercise and nutrition in long-duration spaceflight: Evidence from biochemistry and densitometry. Journal of Bone and Mineral Research. 2012 September; 27(9): 1896-1906. DOI: 10.1002/jbmr.1647. PMID: 22549960.

    Smith SM, Zwart SR, Block G, Rice BL, Davis-Street JE.  The nutritional status of astronauts is altered after long-term space flight aboard the International Space Station. Journal of Nutrition. 2005; 135(3): 437-443. PMID: 15735075.

    Smith SM, Zwart SR.  Nutrition issues for space exploration. Acta Astronautica. 2008; ;63: 609 - 613.: 609-613. DOI: 10.1016/j.actaastro.2008.04.010.

    Smith SM, Heer MA, Shackelford LC, Sibonga JD, Spatz JM, Pietrzyk RA, Hudson EK, Zwart SR.  Bone metabolism and renal stone risk during international space station missions. Bone. 2015 October 8; 81: 712-720. DOI: 10.1016/j.bone.2015.10.002. PMID: 26456109.

    Smith SM, Zwart SR.  Magnesium and space flight. Nutrients. 2015 December 8; 7(12): 10209-10222. DOI: 10.3390/nu7125528. PMID: 26670248.

    Hall PS.  Past and Current Practice in Space Nutrition. Cleveland, OH: Bone Loss During Spaceflight: Etiology, Countermeasures, and Implications for Bone Health on Earth; 2007.

    Smith SM, Zwart SR, Heer MA, Hudson EK, Shackelford LC, Morgan JL.  Men and women in space: Bone loss and kidney stone risk after long-duration spaceflight. Journal of Bone and Mineral Research. 2014 January 28; epub. DOI: 10.1002/jbmr.2185. PMID: 24470067.

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Ground Based Results Publications

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ISS Patents

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Related Publications

    Morgan JL, Heer MA, Hargens AR, Macias BR, Hudson EK, Shackelford LC, Zwart SR, Smith SM.  Sex-specific responses of bone metabolism and renal stone risk during bed rest. Physiological Reports. 2014 August 7; 2(8): e12119-e12119. DOI: 10.14814/phy2.12119.

    Smith SM, Lane HW.  Gravity and space flight: effects on nutritional status. Current Opinions in Clinical Nutrition and Metabolic Care. 1999; 2: 335-338.

    Smith SM, Davis-Street JE, Rice BL, Nillen JL, Gillman PL, Block G.  Nutritional status assessment in semiclosed environments: ground-based and space flight studies in humans. Journal of Nutrition. 2001; 131: 2053-2061.

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Related Websites

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image NASA Image: ISS012E12635 - ISS Science Officer Bill McArthur during expedition 12, during check out of the SLAMMD hardware of HRF-2. Measuring the mass of a crewmember in space is difficult because mass does not equal weight in the absence of gravity.
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